Determination of a preferred beam in a cellular communication network employing signal BeamForming

ABSTRACT

A method for acquiring an indication of a preferred beam of a wireless communication device is disclosed. The method is performed in a network node of a cellular communication network. The network node is adapted to support a plurality of beams of a signal beamforming scheme and to communicate with the wireless communication device using at least one beam of the plurality of beams. The method comprises acquiring a beam power setting of the plurality of beams. The beam power setting comprises a power offset being applied to at least one beam of the plurality of beams, the power offset being relative to a nominal power setting of the plurality of beams. The method also comprises transmitting (to the wireless communication device) a message indicative of the beam power setting, transmitting measurement signals, and receiving (from the wireless communication device) a report indicative of the preferred beam, wherein the preferred beam is determined by the wireless communication device based on the measurement signals and the beam power setting.

TECHNICAL FIELD

The present invention relates generally to the field of signalbeam-forming in cellular communication systems. More particularly, itrelates to determination of a preferred beam in such systems.

BACKGROUND

Beam-forming is a well-known technique in the field of wirelesscommunication. It may, for example, be used for improving thesignal-to-noise ratio (SNR) for a communication link by steering thetransmitted energy in, or collecting the received energy from, afavorable direction. As referred to herein, beam-forming mayconceptually be accomplished by any suitable known or future techniques,and applicable details of those techniques will not be elaborated onfurther.

Determining which beam should preferably be used (e.g. an optimal beamor a sufficiently good beam according to some criteria) in a particularsituation and scenario may be challenging, especially if a large numberof antenna elements and high beam-forming resolution is applied. In atypical implementation of a system using beam-forming, a receivingdevice may perform measurements of reference signals sent from atransmitting device and feed back measurement results (e.g. a preferredbeam).

Precoding is a kind of beam-forming that supports multi-layertransmission in multi-antenna radio systems, such as multiple-inputmultiple-output (MIMO) radio systems, and is relevant in relation to,for example, the 3GPP (Third Generation Partnership Project) standardUniversal Mobile Telecommunication Standard, Long Term Evolution(UMTS-LTE).

Closed loop MIMO precoding is a MIMO approach where each of the multiplestreams are emitted from the transmit antennas (e.g. at a base stationor other network node) with independent and appropriate weighting pereach antenna such that the throughput is ideally maximized between thetransmitting device and the receiving device (e.g. a user equipment (UE)of UMTS-LTE). The precoding weights that should be used are typicallycalculated based on measurements at the receiving device andcommunicated to the transmitting device in a similar manner as explainedabove.

Usually, only a limited number of (predefined) precoding weights areused. The collection of precoding weights is called a codebook. Inclosed loop MIMO precoding, the codebook is typically known at both thetransmitting and the receiving device. Hence, communication of preferredprecoding weights by the receiving device may simply comprise indicatingthe index that the preferred precoding weights have in the codebook.This is typically done by sending a number which is usually called thePrecoding Matrix Indicator (PMI).

SUMMARY

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, or components, but does not preclude thepresence or addition of one or more other features, integers, steps,components, or groups thereof.

It should also be noted that even though precoding and/or MIMO may beused herein to exemplify various embodiments, this is not to beconstrued as limiting. Contrarily, embodiments may be equally applicableto any beam-forming scenario with feed-back information from a receivingdevice.

It is an object of some embodiments to provide a more flexiblebeam-forming system.

According to a first aspect, this is achieved by a method for acquiringan indication of a preferred beam of a wireless communication device,performed in a network node of a cellular communication network.

The network node is adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with the wireless communicationdevice using at least one beam of the plurality of beams.

The method comprises acquiring a beam power setting of the plurality ofbeams, wherein the beam power setting comprises a power offset beingapplied to at least one beam of the plurality of beams, the power offsetbeing relative to a nominal power setting of the plurality of beams.

The method also comprises transmitting (to the wireless communicationdevice) a message indicative of the beam power setting and transmittingmeasurement signals.

The method further comprises receiving (from the wireless communicationdevice) a report indicative of the preferred beam, wherein the preferredbeam is determined by the wireless communication device based on themeasurement signals and the beam power setting.

In some embodiments, the beam power setting may comprise a power offsetvalue per beam in the plurality of beams.

In some embodiments, the plurality of beams may be grouped into aplurality of groups, and the beam power setting may comprise a poweroffset value per group.

The power offset values may comprise any suitable value. For example,one power offset value may be equal to zero (resulting in the nominalpower setting for a beam where that power offset value is applied),and/or one power offset value may be equal to minus the nominal powersetting (resulting in that a beam where that power offset value isapplied is not transmitted—zero power). In some embodiments, the poweroffset values comprise a collection of quantized values between aminimum power offset value and a maximum power offset value. Accordingto some embodiments, the minimum power offset value is not less thanminus the nominal power setting and/or the maximum power offset value isnot larger than zero.

The measurement signals may be transmitted using the nominal powersetting, or any other suitable power setting.

The measurement signals may, for example, comprise reference signalssuch as a cell-specific reference signal (CRS) or a channel-stateinformation reference signal (CSI-RS).

According to some embodiments, the method may further comprise selectingone beam out of the plurality of beams for communication with thewireless communication device based on the received report. For example,the method may comprise selecting the preferred beam for communicationwith the wireless communication device.

The beam power setting may comprise any suitable beam power setting.

In some embodiments, the beam power setting may approximate a cellradiation power profile of the network node. For example, the beam powersetting may be determined by assigning, to each beam in the plurality ofbeams, a power offset value that results in a power setting which isclosest to (a possibly scaled version of) the value of the cellradiation power profile in the direction of the beam. The cell radiationpower profile may be defined as the angular power radiation pattern usedfor transmission of non-user specific signals.

In some embodiments, the beam power setting may comprise beams having apower setting that is lower than the nominal power setting if having adirection within a particular angle range.

The particular angle range may be defined in terms of elevation, azimuthor a combination thereof. The particular angle range may comprise anangle corresponding to a bearing from the network node to a horizonaccording to some embodiments. Alternatively or additionally, theparticular angle range may comprise an angle corresponding to a bearingfrom the network node to a location of a wireless communication deviceserved by a neighboring network node of the cellular communicationsystem according to some embodiments. The location of the wirelesscommunication device served by a neighboring network node of thecellular communication system may, for example, be a probable location,an approximate location, or an actual location.

The direction of a beam may, typically, be defined as the direction ofthe maximum power emission of the beam. According to such a definition,a beam directed 30 degrees below the horizon and having a beam width of90 degrees does not fall within an angle range spanning from 10 degreesabove to 10 degrees below the horizon even though the angle range fallswithin the beam width.

Other beam power settings than those exemplified above are alsopossible.

The message indicative of the beam power setting may have any suitableform and may carry the indication of the beam power setting in anysuitable way.

According to some embodiments, the message indicative of the beam powersetting comprises a value of the power offset (i.e. a relative powervalue, a power offset value) or an indication thereof. The value of thepower offset may be quantized. The value of the power offset may be perbeam, per group, or otherwise. In some embodiments, (vertical and/orazimuth) angular segments are defined and the message indicative of thebeam power setting comprises a value of the power offset per angularsegment.

According to some embodiments, the message indicative of the beam powersetting comprises a power value (i.e. an absolute power value) or anindication thereof. The power value may be quantized. The power valuemay be per beam, per group, or otherwise. In some embodiments, (verticaland/or azimuth) angular segments are defined and the message indicativeof the beam power setting comprises a power value per angular segment.

In some embodiments, the beam power setting may be according to a powerenvelope of a plurality of predetermined power envelopes. Then, themessage indicative of the beam power setting may comprise an envelopeindex identifying the power envelope. Each of the predefined powerenvelopes may comprise a spatial power radiation pattern. For example,the plurality of predefined power envelopes may comprise scaled versionsof the cell radiation power profile.

According to some embodiments, an extended precoding codebook comprisesa plurality of versions of a nominal precoding codebook defining theplurality of beams having the nominal power setting, wherein theplurality of versions define different power offset values. In suchembodiments, the message indicative of the beam power setting maycomprise indices identifying a subset of entries of the extendedprecoding codebook.

A second aspect is a method for determining a preferred beam, performedin a wireless communication device adapted to communicate with a networknode of a cellular communication network.

The network node is adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with the wireless communicationdevice using at least one beam of the plurality of beams.

The method comprises receiving (from the network node) a messageindicative of a beam power setting of the plurality of beams, whereinthe beam power setting comprises a power offset being applied to atleast one beam of the plurality of beams, the power offset beingrelative to a nominal power setting of the plurality of beams.

The method also comprises performing measurements on measurement signalstransmitted by the network node, determining the preferred beam based onthe measurements and the beam power setting, and transmitting (to thenetwork node) a report indicative of the preferred beam.

The message indicative of the beam power setting may comprise a value ofthe power offset according to some embodiments.

In some embodiments, the beam power setting may be according to a powerenvelope of a plurality of predetermined power envelopes and the messageindicative of the beam power setting may comprise an envelope indexidentifying the power envelope.

According to some embodiments, determining the preferred beam maycomprise compensating the measurements based on the beam power settingand selecting the preferred beam based on the compensated measurements.

For example, the measurements relating to a particular beam may bescaled based on the power offset value of that beam in the beam powersetting (e.g. using a scaling factor which is, at least approximately,equal to one plus a ratio of the power offset to the nominal powersetting). Then the scaled measurements may be used to determine thepreferred beam according to any suitable approach (e.g. a currently usedapproach).

Alternatively, a (temporary) scaled codebook may be created from anominal codebook based on the power offset values of the beam powersetting and used instead of the nominal precoding codebook whendetermining the preferred beam based on the measurements.

In some embodiments, an extended precoding codebook may comprise aplurality of versions of a nominal precoding codebook defining theplurality of beams having the nominal power setting, wherein theplurality of versions define different power offset values. Then, themessage indicative of the beam power setting may comprise indicesidentifying a subset of entries of the extended precoding codebook.

In the latter embodiments, the subset of entries of the extendedprecoding codebook may be used instead of the nominal precoding codebookwhen determining the preferred beam based on the measurements.

In some embodiments, the second aspect may additionally have featuresidentical with or corresponding to any of the various features asexplained above for the first aspect, and vice versa.

A third aspect is a computer program product comprising a computerreadable medium, having thereon a computer program comprising programinstructions. The computer program is loadable into a data-processingunit and adapted to cause execution of the method according to any ofthe first and second aspects when the computer program is run by thedata-processing unit.

A fourth aspect is an arrangement for acquiring an indication of apreferred beam of a wireless communication device, the arrangement beingfor a network node of a cellular communication network, wherein thenetwork node is adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with the wireless communicationdevice using at least one beam of the plurality of beams.

The arrangement comprises a controller adapted to cause acquiring of abeam power setting of the plurality of beams, wherein the beam powersetting comprises a power offset being applied to at least one beam ofthe plurality of beams, the power offset being relative to a nominalpower setting of the plurality of beams.

The controller is also adapted to cause transmission (to the wirelesscommunication device) of a message indicative of the beam power setting,and transmission of measurement signals.

The controller is further adapted to cause reception (from the wirelesscommunication device) of a report indicative of the preferred beam,wherein the preferred beam is determined by the wireless communicationdevice based on the measurement signals and the beam power setting.

In some embodiments, the arrangement may further comprise a transmitteradapted to transmit the message indicative of the beam power setting andthe measurement signals, and a receiver adapted to receive the reportindicative of the preferred beam.

In some embodiments, the fourth aspect may additionally have featuresidentical with or corresponding to any of the various features asexplained above for the first aspect.

A fifth aspect is a network node for a cellular communication network(the network node adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with a wireless communicationdevice using at least one beam of the plurality of beams) wherein thenetwork node comprises the arrangement of the fourth aspect.

A sixth aspect is an arrangement for determination of a preferred beam,the arrangement being for a wireless communication device adapted tocommunicate with a network node of a cellular communication network.

The network node is adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with the wireless communicationdevice using at least one beam of the plurality of beams.

The arrangement comprises a controller adapted to cause reception (fromthe network node) of a message indicative of a beam power setting of theplurality of beams, wherein the beam power setting comprises a poweroffset being applied to at least one beam of the plurality of beams, thepower offset being relative to a nominal power setting of the pluralityof beams.

The controller is also adapted to cause measurements being performed onmeasurement signals transmitted by the network node, determination ofthe preferred beam based on the measurements and the beam power setting,and transmission (to the network node) of a report indicative of thepreferred beam.

In some embodiments, the arrangement may further comprise a transmitteradapted to transmit the report indicative of the preferred beam and areceiver adapted to receive the message indicative of the beam powersetting.

In some embodiments, the sixth aspect may additionally have featuresidentical with or corresponding to any of the various features asexplained above for the second aspect.

A seventh aspect is a wireless communication device adapted tocommunicate with a network node of a cellular communication network(wherein the network node is adapted to support a plurality of beams ofa signal beam-forming scheme and to communicate with the wirelesscommunication device using at least one beam of the plurality of beams)wherein the wireless communication device comprises the arrangement ofthe sixth aspect.

An eighth aspect is a cellular communication network comprising at leastone network node according to the fifth aspect and adapted to operate inassociation with at least one wireless communication device according tothe seventh aspect.

An advantage of some embodiments is that a flexible beam-forming systemis enabled. For example, due to the indication of the beam power settingfrom the network node to the wireless communication device and thedetermination by the wireless communication device of the preferred beambased on the beam power setting it is possible to have a dynamic beampower setting and still get accurate preferred beam reports.

Another advantage of some embodiments is that system performance will beimproved compared to a system where all beams use the nominal powersetting. The system performance will also be improved compared to asystem where power offsets may be applied to one or more beams and thewireless communication device assumes nominal power setting whendetermining the preferred beam.

Yet another advantage of some embodiments is that the amount of overheadsignaling is fairly low. This is particularly true for the embodimentswhere the indication of the beam poser setting comprises an envelopeindex.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the followingdetailed description of embodiments, with reference being made to theaccompanying drawings, in which:

FIG. 1 is a combined flowchart and signaling diagram illustratingexample method steps and signals according to some embodiments;

FIG. 2 is a schematic drawing illustrating example scenarios accordingto some embodiments;

FIG. 3 is a schematic drawing illustrating example beam-formingaccording to some embodiments;

FIG. 4 is a block diagram illustrating an example arrangement accordingto some embodiments;

FIG. 5 is a block diagram illustrating an example arrangement accordingto some embodiments; and

FIG. 6 is a schematic drawing illustrating a computer readable mediumaccording to some embodiments.

DETAILED DESCRIPTION

In the following, embodiments will be described where flexiblebeam-forming is enabled.

Studies have shown that controlling the power used by each beam of abeam-forming system may improve the overall performance of the system.

For example, it may be beneficial to reduce the power used by a beamthat is directed towards a wireless communication device served by aneighboring network node (and thereby experiencing the power of thatbeam as interference), or to completely avoid using such beams. Removingsome precoding vectors from a codebook can be done in UMTS-LTE by usingcodebook subset restriction as specified in 3GPP technical specification36.211 version 12.6.0.

The location of wireless communication devices served by neighboringnetwork nodes may be determined explicitly, approximately, orprobability-wise (e.g. based on statistics). Alternatively oradditionally, beams directed (at least approximately) towards thehorizon may use a reduced power setting.

Of course, numerous other beam power settings are possible. Furthermore,the beam power setting may be changed dynamically as conditions changes.

Determining which beam should preferably be used for communication (e.g.an optimal beam or a sufficiently good beam according to some criteria)in a particular situation and scenario may be challenging. In a typicalimplementation of a system using beam-forming, a receiving device mayperform measurements of reference signals sent from a transmittingdevice and feed back measurement results (e.g. a preferred beam).

If the wireless communication device potentially receiving the prospecttransmission of a beam presumes a nominal beam power setting whendetermining which beam it prefers, the determination of the preferredbeam might be sub-optimal if the beam—once selected—is transmitted usingan other than nominal power setting. For example, using a nominalprecoding codebook when determining the preferred beam might results ina non-optimal PMI report.

Thus, to adequately determine the preferred beam the wirelesscommunication device needs information regarding the beam power settingto be used for the beam-forming transmission. This information is,according to embodiments described herein, conveyed from the networknode to the wireless communication device via a message indicative ofthe beam power setting.

FIG. 1 illustrates example methods 110, 150 carried out by,respectively, a network node (NWN) 111 of a cellular communicationnetwork and a wireless communication device (WCD) 151 and signals sentthem between according to some embodiments.

The network node 111 is adapted to support a plurality of beams of asignal beam-forming scheme and to communicate with the wirelesscommunication device 151 using at least one beam of the plurality ofbeams. It is assumed that the network node applies a beam power settingin which a power offset (which may be zero) relative to a nominal powersetting is applied to at least one beam of the plurality of beams.

The method 110 is for acquiring an indication of a preferred beam of thewireless communication device and the method 150 is for determining apreferred beam.

Of course, method 150 is also applicable for determining more than onepreferred beam, i.e., a set of beams which fulfill some pre-determinedpreferred beam criteria.

In step 112, the network node acquires (e.g. determines autonomously orreceives information about) a beam power setting of the plurality ofbeams.

As elaborated on above, there are numerous variations to the beam powersetting. For example, the beam power setting may comprise beams having apower setting that is lower than the nominal power setting if having adirection within a particular angle range. The particular angle rangemay comprise an angle corresponding to a bearing from the network nodeto a location of a wireless communication device served by a neighboringnetwork node of the cellular communication system. Alternatively oradditionally, the beam power setting may approximate a cell radiationpower profile of the network node.

A message 134 indicative of the beam power setting is transmitted by thenetwork node 111 in step 114 and received by the wireless communicationdevice in step 154. This message may be communicated when the wirelesscommunication device registers at the network node, when the beam powersetting changes, at regular intervals, and/or at any other suitablepoint in time.

As elaborated on above, there are numerous variations to the messageindicative of the beam power setting. For example, the message 134 maycomprise a (quantized) value of the power offset, an envelope indexidentifying one of a plurality of predetermined power envelopes, orindices identifying a subset of entries of an extended precodingcodebook.

In step 116, the network node 111 transmits measurement signals 136. Themeasurement signals may be any signals suitable for measurement, forexample, reference signals (CSI-RS or CRS) or some other non-dedicatedsignals. Typically, but not necessarily, the measurements signals aretransmitted using the same transmit power.

The wireless communication device 151 performs measurements on themeasurement signals in step 156 and determines a preferred beam in step158 based on the measurements and the beam power setting.

As elaborated on above, determining the preferred beam may comprisecompensating (e.g. scaling) the measurements based on the beam powersetting and selecting the preferred beam based on the compensatedmeasurements, or using a subset of entries of an extended precodingcodebook when selecting the preferred beam based on the measurements.

The wireless communication device 151 transmits a report 140 (e.g. a PMIreport) indicative of the preferred beam in step 160, which report isreceived by the network node 111 in step 120.

The network node 111 may use the received report to select one of theplurality of beams (e.g. the preferred beam) for communication with thewireless communication device as illustrated by step 122.

FIG. 2 illustrates an example scenario where some embodiments may beapplicable. A network node 211 communicates with two wirelesscommunication devices 251, 252 using the beams 212 and 213,respectively, and a neighboring network node 221 communicates with awireless communication device 253.

FIG. 2 illustrates a situation where the wireless communication device253 communicating with the neighboring network node 221 experiences thebeam 213 as interference (illustrated by 213′) since the beam 213 isdirected towards the wireless communication device 253. In such asituation, it may be beneficial to let the beam 213 use a lower powerlevel than the beam 212 to reduce interference in the system and improveoverall performance.

A cloud service 200, adapted to communicate with the network node 211 isalso illustrated in FIG. 2. The cloud service may, for example, providelocation information regarding wireless communication devices and/ordetermine and provide the beam power setting.

FIG. 3 illustrates example beam-forming according to some embodiments. Anominal beam power setting with equal power 320 for all beams 310 isillustrated in the left part of the figure. The middle part of thefigure shows a power envelope 330, which may, for example be a cellradiation pattern. The right part of the figure illustrates how offsetsmay be applied to the beams 340 to achieve a beam power setting 300which has (approximately) the same shape as (a possibly scaled versionof) the power envelope 330′.

FIG. 4 illustrates an example arrangement 400 for a network node of acellular communication network according to some embodiments. Thenetwork node may, for example, be the network node 111 of FIG. 1 and isadapted to support a plurality of beams of a signal beam-forming schemeand to communicate with a wireless communication device using at leastone beam of the plurality of beams.

The arrangement 400 is for acquiring an indication of a preferred beamof a wireless communication device and comprises a controller (CNTR) 420adapted to cause execution of the method 110 as described in connectionto FIG. 1.

The arrangement 400 may also comprise a transmitter and a receiver(illustrated in FIG. 4 as a transceiver (RX/TX) 410) adapted to transmitthe message indicative of the beam power setting and the measurementsignals (compare, respectively, with steps 114 and 116 of FIG. 1), andreceive the report indicative of the preferred beam (compare with step120 of FIG. 1).

The controller 420 may comprise various modules to cause the executionof the method 110. For example, the controller 420 may comprise one ormore of a beam power setting module (BPS) 421, a beam selector (SEL)422, a codebook module (CB) 423, and a power envelope module (ENV) 424.

The beam power setting module 421 may be adapted to acquire (e.g.determine or receive) and store the beam power setting to be applied(compare with step 112 of FIG. 1).

The selector 422 may be adapted to select the beam to be used forcommunication based on the received report (compare with step 122 ofFIG. 1).

The codebook module 423 may be adapted to store a (possibly extended)codebook. Alternatively or additionally, the codebook module 423 may beadapted to determine indices defining a subset of an extended codebookbased on the beam power profile to be used.

The power envelope module 424 may be adapted to store a collection ofpredetermined power envelopes. Alternatively or additionally, the powerenvelope module 424 may be adapted to determine an index defining apower envelope based on the beam power profile to be used.

FIG. 5 illustrates an example arrangement 500 for a wirelesscommunication device according to some embodiments. The wirelesscommunication device may, for example, be the wireless communicationdevice 151 of FIG. 1 and is adapted to communicate with a network nodesupporting a plurality of beams of a signal beam-forming scheme.

The arrangement 500 is for determining a preferred beam of the wirelesscommunication device and comprises a controller (CNTR) 520 adapted tocause execution of the method 150 as described in connection to FIG. 1.

The arrangement 500 may also comprise a transmitter and a receiver(illustrated in FIG. 5 as a transceiver (RX/TX) 510) adapted to receivethe message indicative of the beam power setting (compare with step 154of FIG. 1), and transmit the report indicative of the preferred beam(compare with step 160 of FIG. 1).

The controller 520 may comprise various modules to cause the executionof the method 150. For example, the controller 520 may comprise one ormore of a beam power setting module (BPS) 521, a measurement module(MEAS) 525, a preferred beam determiner (DET) 522, a codebook module(CB) 523, and a power envelope module (ENV) 524.

The beam power setting module 521 may be adapted to store the receivedbeam power setting (compare with step 112 of FIG. 1).

The measurement module 525 may be adapted to perform measurements(compare with step 156 of FIG. 1).

The preferred beam determiner 522 may be adapted to determine apreferred beam based on the measurements and the beam power setting(compare with step 158 of FIG. 1) according to any approach describedabove.

The codebook module 523 may be adapted to store a (possibly extended)codebook. Alternatively or additionally, the codebook module 523 may beadapted to provide a subset of an extended codebook based on thereceived beam power setting.

The power envelope module 524 may be adapted to store a collection ofpredetermined power envelopes. Alternatively or additionally, the powerenvelope module 524 may be adapted to provide a power envelope based onthe received beam power setting.

Three different examples of how the message indicative of the beam powersetting may be implemented will now be given.

In the first example, an extended codebook is created that comprisemultiple versions of a nominal codebook, where each version hasdifferent power offset from the nominal power (power offset zero). Inthis example, the codebook subset restriction functionality alreadyavailable in UMTS-LTE may be used to select a subset of the extendedcodebook such that the subset (at least approximately) matches the beampower setting to be used. In this way, the wireless communication devicewill implicitly receive the beam power setting and can make an accuratedetermination of the preferred beam.

The extended codebook could be standardized and would then beimplemented in all wireless communication devices and network nodes.Alternatively, the extended codebook could be implemented in networknodes and the network nodes could signal during operation how theextended codebook should be designed. For example, the network nodecould signal a number of power offsets to be applied to the nominalcodebook. An advantage with the former solution is that no extrasignaling is needed to define the extended codebook. An advantage withthe latter solution is that the beam power setting is less restrictive;the network node can use power offsets that it actually needs to, forexample, get a desired shape of the envelope of the beams.

In the second example, the network node signals the power offset usedfor each beam to the wireless communication device. Thus, the networknode may inform the wireless communication device about deviation(offset) of the power setting from the nominal power setting forrespective beams. In order to reduce the overhead signaling it ispreferred that the power offsets are quantized. For example, if thenetwork node uses four different power settings per beam, it is enoughto signal 2 bits per beam to inform the wireless communication device.

According to some aspects, the used beam power setting is assumed to berather static in time. In such cases, the signaling of the power offsettypically has to be done only once (or very seldom) per wirelesscommunication device. If the beam power setting is the same for allwireless communication devices of a cell, the signaling of the poweroffset may even be done only once (or very seldom) per cell (e.g. viabroadcast). Hence, this approach does not require much signalingoverhead.

In the third example, envelope shapes of the beams are defined. Forexample, each envelope shape may have a certain power offset forrespective PMI. The envelope shapes and their corresponding power offsetper PMI is known both at the network node and at the wirelesscommunication device. Thus, the network node only has to inform thewireless communication device about which envelope shape is applied.This solution typically requires very little overhead signaling at theexpense of being less flexible than the second example.

The described embodiments and their equivalents may be realized insoftware or hardware or a combination thereof. They may be performed bygeneral-purpose circuits associated with or integral to a communicationdevice, such as digital signal processors (DSP), central processingunits (CPU), co-processor units, field-programmable gate arrays (FPGA)or other programmable hardware, or by specialized circuits such as forexample application-specific integrated circuits (ASIC). All such formsare contemplated to be within the scope of this disclosure.

Embodiments may appear within an electronic apparatus (such as awireless communication device or a network node) comprisingcircuitry/logic or performing methods according to any of theembodiments.

According to some embodiments, a computer program product comprises acomputer readable medium such as, for example, a USB-stick, a plug-incard, an embedded drive, or a read-only memory (ROM) such as the CD-ROM600 illustrated in FIG. 6. The computer readable medium may have storedthereon a computer program comprising program instructions. The computerprogram may be loadable into a data-processing unit (PROC) 620, whichmay, for example, be comprised in a wireless communication device or anetwork node 610. When loaded into the data-processing unit, thecomputer program may be stored in a memory (MEM) 630 associated with orintegral to the data-processing unit. According to some embodiments, thecomputer program may, when loaded into and run by the data-processingunit, cause the data-processing unit to execute method steps accordingto, for example, any of the methods shown in FIG. 1.

Reference has been made herein to various embodiments. However, a personskilled in the art would recognize numerous variations to the describedembodiments that would still fall within the scope of the claims. Forexample, the method embodiments described herein describes examplemethods through method steps being performed in a certain order.However, it is recognized that these sequences of events may take placein another order without departing from the scope of the claims.Furthermore, some method steps may be performed in parallel even thoughthey have been described as being performed in sequence.

In the same manner, it should be noted that in the description ofembodiments, the partition of functional blocks into particular units isby no means limiting. Contrarily, these partitions are merely examples.Functional blocks described herein as one unit may be split into two ormore units. In the same manner, functional blocks that are describedherein as being implemented as two or more units may be implemented as asingle unit without departing from the scope of the claims.

Hence, it should be understood that the details of the describedembodiments are merely for illustrative purpose and by no meanslimiting. Instead, all variations that fall within the range of theclaims are intended to be embraced therein.

The invention claimed is:
 1. A method, performed in a network node of acellular communication network, for acquiring an indication of apreferred downlink transmit beam of a wireless communication device fordownlink transmissions from the network node, wherein the network nodeis configured to support a plurality of beams of a signal beam-formingscheme and to communicate with the wireless communication device usingat least one downlink transmit beam of the plurality of beams, themethod comprising: acquiring a beam power setting of the plurality ofbeams, wherein the beam power setting comprises a power offset beingapplied at the network node to at least one downlink transmit beam ofthe plurality of beams for downlink transmissions from the network node,the power offset being relative to a nominal power setting of theplurality of beams; transmitting, to the wireless communication device,a message indicative of the beam power setting; transmitting measurementsignals; and receiving, from the wireless communication device, a reportindicative of the preferred downlink transmit beam, wherein thepreferred downlink transmit beam is determined by the wirelesscommunication device based on the measurement signals and the beam powersetting.
 2. The method of claim 1, further comprising selecting onedownlink transmit beam out of the plurality of beams for downlinkcommunication with the wireless communication device based on thereceived report.
 3. The method of claim 1, wherein the beam powersetting approximates a cell radiation power profile of the network node.4. The method of claim 1, wherein the beam power setting comprises beamshaving a power setting that is lower than the nominal power setting ifhaving a direction within a particular angle range.
 5. The method ofclaim 4, wherein the particular angle range comprises an anglecorresponding to a bearing from the network node to a location of awireless communication device served by a neighboring network node ofthe cellular communication system.
 6. The method of claim 1, wherein themessage indicative of the beam power setting comprises a value of thepower offset.
 7. The method of claim 1: wherein an extended precodingcodebook comprises a plurality of versions of a nominal precodingcodebook defining the plurality of beams having the nominal powersetting, wherein the plurality of versions define different power offsetvalues; and wherein the message indicative of the beam power settingcomprises indices identifying a subset of entries of the extendedprecoding codebook.
 8. A method for determining a preferred downlinktransmit beam, performed in a wireless communication device adapted tocommunicate with a network node of a cellular communication network,wherein the network node is configured to support a plurality of beamsof a signal beam-forming scheme and to communicate with the wirelesscommunication device using at least one downlink transmit beam of theplurality of beams, the method comprising the wireless communicationdevice: receiving, from the network node, a message indicative of a beampower setting of the plurality of beams, wherein the beam power settingcomprises a power offset being applied at the network node to at leastone downlink transmit beam of the plurality of beams for downlinktransmissions from the network node, the power offset being relative toa nominal power setting of the plurality of beams; performingmeasurements on measurement signals transmitted by the network node;determining the preferred downlink transmit beam based on themeasurements and the beam power setting; and transmitting, to thenetwork node, a report indicative of the preferred downlink transmitbeam.
 9. The method of claim 8, wherein the determining the preferreddownlink transmit beam comprises: compensating the measurements based onthe beam power setting; and selecting the preferred downlink transmitbeam based on the compensated measurements.
 10. The method of claim 8:wherein an extended precoding codebook comprises a plurality of versionsof a nominal precoding codebook defining the plurality of beams havingthe nominal power setting, wherein the plurality of versions definedifferent power offset values; and wherein the message indicative of thebeam power setting comprises indices identifying a subset of entries ofthe extended precoding codebook.
 11. A non-transitory computer readablerecording medium storing a computer program product for controlling anetwork node of a cellular communication network for acquiring anindication of a preferred downlink transmit beam of a wirelesscommunication device for downlink transmissions from the network node,wherein the network node is configured to support a plurality of beamsof a signal beam-forming scheme and to communicate with the wirelesscommunication device using at least one downlink transmit beam of theplurality of beams, the computer program product comprising softwareinstructions which, when run on processing circuitry of the networknode, causes the network node to: acquire a beam power setting of theplurality of beams, wherein the beam power setting comprises a poweroffset being applied at the network node to at least one downlinktransmit beam of the plurality of beams for downlink transmissions fromthe network node, the power offset being relative to a nominal powersetting of the plurality of beams; transmit, to the wirelesscommunication device, a message indicative of the beam power setting;transmit measurement signals; and receive, from the wirelesscommunication device, a report indicative of the preferred downlinktransmit beam, wherein the preferred downlink transmit beam isdetermined by the wireless communication device based on the measurementsignals and the beam power setting.
 12. A non-transitory computerreadable recording medium storing a computer program product fordetermining a preferred downlink transmit beam by a wirelesscommunication device adapted to communicate with a network node of acellular communication network, wherein the network node is configuredto support a plurality of beams of a signal beam-forming scheme and tocommunicate with the wireless communication device using at least onedownlink transmit beam of the plurality of beams, the computer programproduct comprising software instructions which, when run on processingcircuitry of the wireless communication device, causes the wirelesscommunication device to: receive, from the network node, a messageindicative of a beam power setting of the plurality of beams, whereinthe beam power setting comprises a power offset being applied at thenetwork node to at least one downlink transmit beam of the plurality ofbeams for downlink transmissions from the network node, the power offsetbeing relative to a nominal power setting of the plurality of beams;perform measurements on measurement signals transmitted by the networknode; determine the preferred downlink transmit beam based on themeasurements and the beam power setting; and transmit, to the networknode, a report indicative of the preferred downlink transmit beam. 13.An arrangement for acquiring an indication of a preferred downlinktransmit beam of a wireless communication device, the arrangement beingfor a network node of a cellular communication network, wherein thenetwork node is adapted to support a plurality of beams of a signalbeam-forming scheme and to communicate with the wireless communicationdevice using at least one downlink transmit beam of the plurality ofbeams, the arrangement comprising: processing circuitry; memorycontaining instructions executable by the processing circuitry wherebythe arrangement is operative to: acquire of a beam power setting of theplurality of beams, wherein the beam power setting comprises a poweroffset being applied at the network node to at least one downlinktransmit beam of the plurality of beams for downlink transmissions fromthe network node, the power offset being relative to a nominal powersetting of the plurality of beams; transmit, to the wirelesscommunication device, a message indicative of the beam power setting;transmit measurement signals; and receive, from the wirelesscommunication device, of a report indicative of the preferred downlinktransmit beam, wherein the preferred downlink transmit beam isdetermined by the wireless communication device based on the measurementsignals and the beam power setting.
 14. An arrangement for determinationof a preferred downlink transmit beam, the arrangement being for awireless communication device adapted to communicate with a network nodeof a cellular communication network, wherein the network node is adaptedto support a plurality of beams of a signal beam-forming scheme and tocommunicate with the wireless communication device using at least onedownlink transmit beam of the plurality of beams, the arrangementcomprising: processing circuitry; memory containing instructionsexecutable by the processing circuitry whereby the arrangement isoperative to: receive, from the network node, of a message indicative ofa beam power setting of the plurality of beams, wherein the beam powersetting comprises a power offset being applied at the network node to atleast one downlink transmit beam of the plurality of beams for downlinktransmissions from the network node, the power offset being relative toa nominal power setting of the plurality of beams; perform measurementson measurement signals transmitted by the network node; determine of thepreferred downlink transmit beam based on the measurements and the beampower setting; and transmit, to the network node, of a report indicativeof the preferred downlink transmit beam.
 15. A wireless communicationdevice adapted to communicate with a network node of a cellularcommunication network, wherein the network node is adapted to support aplurality of beams of a signal beam-forming scheme and to communicatewith the wireless communication device using at least one downlinktransmit beam of the plurality of beams, the wireless communicationdevice comprising: processing circuitry; memory containing instructionsexecutable by the processing circuitry whereby the wirelesscommunication device is operative to: receive, from the network node, ofa message indicative of a beam power setting of the plurality of beams,wherein the beam power setting comprises a power offset being applied atthe network node to at least one downlink transmit beam of the pluralityof beams for downlink transmissions from the network node, the poweroffset being relative to a nominal power setting of the plurality ofbeams; perform measurements on measurement signals transmitted by thenetwork node; determine of a preferred downlink transmit beam based onthe measurements and the beam power setting; and transmit, to thenetwork node, of a report indicative of the preferred downlink transmitbeam.